2 Questions answered
What is the recommended frequency for getting an STD test check up?
The recommended frequency of STD testing will vary for different individuals. If you have had your testing performed 6 months ago, and have not had ANY sexual partners since, then I would say it is not really necessary to test unless you have any symptoms of concern. However, if you have had sexual intercourse with a known partner but no NEW sexual partners as you mentioned, then your decision to test would depend on whether you have concerns about your partner's status.
What are the implications if I am a non-responder to the hepatitis B vaccination?
Hepatitis B vaccination usually requires a series of 3 injections over a 6-month period. A single 'booster' vaccine may not be adequate for antibody response. However, if you have completed two full rounds of the Twinrix vaccine and currently still do not have detectable antibody levels, then you would be termed a non-responder.